Method of and apparatus for heating oil or petroleum to elevated temperatures



Sept. 6, 1938. F. H. PRAEGER 2,129,589

METHOD OF AND APPARATUS FOR HEATING OIL OR PETROLEUM TO ELEVATED TEMPERATURES Filed NOV. 22, 1930 5 sheetssheet l Q Q QOOOOOQ o? A TTORNEY.

F. H. PRAEGER 2,129,589 METHOD OF AND APPARATUS FOR HEATING OIL OR PETROLEUM TO ELEVATED TEMPERATURES Filed Nov. 22, 1930 5 Sheets-Sheet 2 Sept. 6, 1938.

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5 Sheets-Sheet 5 F. H. PR-AEGER METHOD OF AND APPARATUS FOR HEATING OIL OR PETROLEUM TO ELEVATED TEMPERATURES Filed NOV. 22, 1930 OOOOOOOOOO O O O O O O O O O O O O O O O 0 O O O 0 OOOOOOOOOO O O O 0 O f j /wmg Sept. 6, 1938.

i w j vPatented Sept. 6, 1938 METHOD OF AND APPARATUS FOR HEATING OIL OR PETROLEUM TO ELEVATED TEM- PERATURES Frank H. Praeger, Tulsa, Okla., assignor, by

mesne assignments, to Alcorn Combustion Company, Philadelphia, Pa., a corporation of Delaware Application November 22, 1930, Serial No. 497,553

50 Claims. (Cl. 1236-47) My invention relates to systems for effecting 4transfer of heat to absorption structure, in-

cluding that utilized in heating, distilling or cracking petroleum.

In accordance with my invention, in a heat transfer system in which the ratio between the heat transferred by radiation andthe heat transferred by convection is materially different in different zones, heat absorption structure, as one or more rows or tiers of tubes, is disposed below the path of the burning gases and/ or hot products of. combustion to effect high overall average rate of heat' transfer with small or no material difference between the temperatures of the heat absorption structures of the. diierent zones; preferably, combustion is begun in a furnace chamber and the burning gases and/or hot products of combustion from that chamber pass above the aforesaid heat absorption structure which absorbs heat preponderantly or substantially solely by radiation, before contacting with, or transferring any material quantity of heat by convection to, any of the other heat absorption structure of the system.

More specifically, the tubes below the path of the gases are disposed adjacent or upon the floor of a furnace chamber avoiding need of supporting structure in position to reduce the tube surface presented to the flame or heat-radiating walls of. the chamber.

Further in accordance with my invention, oil, as petroleum or a component or product thereof, is passed, during any suitable heat treatment, including simple heating, fractional distillation, or destructive distillation or cracking, through the aforesaid heat absorption structure, and subsequently, or previously, or both, to other heat absorption structure to which heat is transferred by radiation,` or convection, or both.

In accord with further aspects of my invention, oil-heating systems may include a plurality of separate or individual heating chambers or zones in which aremaintained currents of hot combustion gases individual thereto, and individual to heat absorption structure adjacent to, as upon the oor of each heating chamber, but below and without the currents of hot combustion gases or flame, and receiving heat substantially solely by radiation; and auxiliary combustion chambers may be provided in which combustion of. fuel may be begun and partially or wholly completed before the entry of the hot products of combustion or flame into the heating chambers. My invention resides in the method, system and apparatus of the character hereinafter described and claimed.

For an understanding of my invention and for illustration of some of the forms it may take, reference is to be had to the accompanying drawings, in which:

Fig. 1 is an elevational view in section, of heat transfer apparatus embodying my invention.

Figs. 2 to 10 inclusive are, respectively, vertical sectional views of other modified forms or types of my heat transfer structure, while Fig. 3A is a sectional view taken on the line 3A-3A of Fig. 3.

Referring to Fig. 1, the walls I of the furnace and the arch 2 may be of. fire-brick, or equivalent. Within the radiation combustion chamber 3, having walls of silicon carbide, or other highly refractory material whose heat conductivity is materially higher than fire-brick or kindred material, may be eifected combustion of any suitable material, solid or fluid. Specifically, gas or oil, or both, supplied to the burner I, generally under high pressure, is mixed with air flowing through the duct 5 and the mixture burner Within chamber 3, the combustion progressing as the fuel, air and gases pass through the chamber. The arrangement of the burner, the combustion chamber and intervening Venturi block 3a, is more fully described and claimed in co-pending application Serial No. 361,290, filed May 8, 1929, now Patent No. 1,888,804, dated November 22, 1932. It will be understood that more than one burner and combustion chamber may be employed for heating the zone A.

Part of the heat of combustion is utilized to raise the temperature of the refractory walls of chamber 3 to a high temperature to effect suitable rate of radiation of heat to tubes 6 above the combustion chamber and within the zone or region A. The furnace walls within this zone are also heated by radiation from the combustion chamber and re-radiate to the tubes 6. The hot gases of combustion are substantially excluded from this region or zone or from convectively heating tubes 6 which receive heat substantially solely by radiation.

The burninggases pass from the chamber 3 through the perforated arch 2 into the region or zone B and thence through the zone C to the stack duct S. The tubesv within zone C constitute a second heat absorption structure to which heat is transferred by convection. The upper tubes of the zone B are heated preponderantly by convection while the lower tubes receive heat both by convection from the gases and by radiation from the arch 2 and the ame below it. As these lower tubes of zone B are heated both by radiation and convection, their temperature may become excessive, and in any event their temperature is the limiting factor determining the safe operating capacity of the furnace or system as a whole.

In accordance with my. invention, heat absorption structure, as tubes II, is disposed below the path of gases discharged from the chamber 3 and receives heats preponderantly or practically solely by radiation fromA the combustion gases or flame and exposed refractory, to reduce the temperature of the gases before they come into contact with the lower tubes in zone B so materially that the temperature of these tubes does not become excessive.

'Though the tubes II are within a fire chamber through which the hot gases, burning mixture or flames pass, nevertheless they are for the greater part or substantially entirely out of the stream of natural flow; they are not to material extent washed or contacted by the moving gases, flame or burning mixture, and are, therefore, but slightly, if at all, convectively heated. 'I'hey absorb heat preponderantly or substantially solely by radiation from the gases or flames projected over and above them, and from the adjacent wall structure which may attain high temperature. Since these tubes receive heat principally by radiation, the application of. heat is well distributed over the exposed surface of the tubes, preventing high rate of heat input through restricted areas; in contradistinction from convection heating by a stream of gases which necessarily contact with a tube along a line or restricted area, resulting in local overheating within the restricted area of the tube or heat absorption structure itself, and/or of the material contained in or passing .through it.

As a result of use of tubes II, the safe operating capacity of the furnace is increased to substantial extent, as for example, from 25% to 50%, with little or no increase of furnace temperature, and for comparatively slight increase in area of heat absorption surface. By way of example only, the addition of six tubes II to a furnace similar to that of Fig. 1, representing an increase of less than 10% in heat absorption area, permitted a 50% increase in oil throughput in a cracking system for petroleum without appreciable increase oi the furnace temperature. Further, the economy or efiiciency of operation is high, as there is no need of diminishing or restricting the application ofeither radiant the combustion rate may be materially increased, materially to increase the throughput, yet the temperature of the lower tubes in zone B will not be appreciably higher and may even be less than the temperature they would attain for lower throughputs without tubes II. 'I'his because with the oor tubes, the average heat input per unit area of heat absorption surface per unit of'time may 'be increased without attainment of excessively high temperature by the heat-absorption structure of any of the zones or regions, and without marked difference between the temperatures of the different heat absorption structures.

f The sequence in which the oil under treatment may traverse the tubes of the different sections may be whatever desired. Specifically, the incoming oil may enter the top row of tubes in the zone C, pass through the lower rows in succession, then through the tubes II'to lower row of tubes in section B to the top row of tubes in section B, downwardly through the other rows in section B, and thence to the lower row of tubes 6 in zone A; the oil passing out of the furnace from one end of the upper row of tubes in zone A as indicated.

The tubes II are designated floor tubes whether they be placed upon or near the furnace iioor, as shown, or Votherwise and equivalently located below the hot gases issuing from chamber 3 or from some other chamber or region as hereinafter described in connection with other forms of my invention.

In the type of furnace shown in Fig. 2, 'the tubes 6 absorb heat substantially solely by radiation from the refractory walls of the combustion chamber 3 and the wall structurel of the zone A. The burning gases and hot products of combustion leave the open end of the chamber 3 passing through the furnace to stack S. The tubes 8 in zone C are heated preponderantly by convection from the hot gases, while the tubes 9 of zone B are heated both by convection and by radiation from the flamev and from the wall structure exposed thereto. Since tubes 9 are heated both by convection and radiation their temperature may be excessive, though the temperatures of the tubes 6 and 8 may be well below safe operating values. By the addition of the tubes II, disposed for example upon the furnace floor, below the path of the gases leaving the combustion chamber 3, the temperature of the gases is reduced to such extent -that although the tubes 9 of zone B are heated both by radiation and convection, their temperature nevertheless does not become excessive and does not materially exceed that of the other absorption structure of the furnace. Consequently, the rate .of combustion may be materially increased to effect or permit higher throughput, without exceeding the safe temperature limit of any of the absorption structures, since the absorption of heat is more uniformly distributed than before. In other words, though the average heat input per unit of heat absorbing area is materially higher than heretofore realized, greatly increased capacity of the system is effected, without exceeding safe operating limits, by so distributing the absorption of heat in the different zones, that the temperature of any one zone does not greatly or materially differ from the temperature of any of the other zones, and this equalization is effected by the use of the tubes I I disposed within the fire chamber below the path of the gases leaving the combustion chamber 3, and heated largely or substantially solely by radiation.

Oil may flow through the tubes of the different sections or zones in any desired sequence; for example, it may flow through the tubes 8 of section C, thence through the tubes I I, then through the tubes 8 of section B, and finally through the tubes 6 of section A.

Referring to Fig. 3, the top, bottom and side walls I maybe of brick Work or equivalent, the bottom having one or more raised portions for supporting one or more combustion chambers 3, five being shown in Fig. 3A, by way of example. Part of the heat of combustion is utilized to raise the temperature of the refractory walls of chambers 3 to suitably high temperature to effect suitable rate of radiation of heat to tubes 6v above the combustion chambers andwithin the zone or region A defined by the partition 1. The

furnace walls within this zone are also heated by radiation from the combustion chambers and re-radiate to the tubes 6 or equivalent heat absorption structure. The hot gases of combustion are more or less excluded from this region or zone and in any event do not materially heat the tubes 6 which receive heat substantially solely by radiation.

The hot and burning gases or products pass from chambers 3 into and through the region or zone B into and through the zone C around and between the tubes 8 to, for example, the stack S. The tubes 8 within zone C constitute a second heat absorption structure to which heat is transferred by convection.

The tube 9 at the top of the zone B and the tubes I at one end of the zone against or adjacent the side wall receive heat both by radiation from the combustion gases and the lining of the furnace and by convection from the gases. The tubes iI are disposed upon or adjacent the bottom or oor of the furnace to receive heat practically solely by radiation from the combustion gases and the furnace lining, and so materially reduce the temperature of the gases that the temperature of tubes 9 and I0 does not become excessive though they absorb heat both by radiation and convection. f

The use of the auxiliary combustion chambers 3 in connection with the floor tubes I I is particularly advantageous in a furnace in which the relationship of the chambers and the floor tubes is of the character herein disclosed, as for example, in Fig. 3. In my arrangement, the auxiliary combustion chambers 3 serve to guide the currents of combustion gases outwardly over and above the floortubes, eiecting a longer gas travel and making possible a more extensive or Wider bank of :door tubes. This arrangement is to be contrasted with the use of simple open burners in which the gases and fuel products immediately adjacent the burner, where combustion has not yet been initiated or is taking place at a relatively low rate, are at a relatively low temperature or actually cold, so that the oor tubes immediately adjacent the burner are not heated to any substantial degree. By the use of the auxiliary combustion chambers, however, the combustion of the fuel is initiated and partially or wholly completed therein so that the gases emerging therefrom are at or near theirmaximum temperature and are thus effective radiantly to heat the floor tubes immediately adjacent the combustion chambers. In fact, the rate of heat transfer per unit area to the floor tubes is substantially equalized throughout the bank of tubes. Moreover, since combustion has been initiated and partially or wholly completed before the hot combustion gases are discharged from the combustion chambers 3, the cooling effect of the oor tubes is insufficient to prevent complete combustion, which might be the case if an open burner were used.

The oil may flow through the tube sections of the furnace of Fig. 3 in any desired sequence; for example, it may first traverse the tubes 8 of zone C, then the tubes 6 of zone A, then the tubes 9 and I0 of zone B, and finally the tubes II, as indicated.

In the type of furnace shown in Fig. 4, the combustion reaction progresses at least to a substantial degree within the chamber I2 and the ame and hot gases pass upwardly into the chamber D, the gases passing through the ports in the partition or barrier I4 into chamber E, and thence downwardly through zones or chambers E and F to the stack duct I5 or other destination.

The tubes I6 at the top of chamber D receive heat practically solely by radiation from the flame and the refractory lining of the chamber. Tubes I1 within zone or chamber F receive heat preponderantly by convection from the gases while tubes lilv within zone or chamber E receive heat by radiation from the barrier I4 and other refractory lining of this chamber and also by convection from thegases ilowing to the stack.

By disposing tubes I9 below and out of the path of the hot gases and ame, as adjacent or upon the floor of fire chamber D, they absorb heat chiefly by radiation and so reduce the temperature to which the tubes I6 particularly are subjected, and to a lesser extent, the temperature of tubes I8. The tubes I6 have no appreciable efl'ect upon the temperature of tubes I9. The safe capacity or throughput is increased with no increase of temperature within chamber D. The number of tubes I 9 necessary to effect marked increase of capacity is small, and in any event, the number of. these tubes, or equivalent absorbing surface, should not be so large as to reduce the temperature within chamber D to such extent that combustion will not be c omplete; and the same applies to other disclosed forms of my invention in which the combustion is not substantially completed prior to passage of the gases into the chamber containing the floor tubes.

The tube sections may be connected to effect flow of oil therethrough in any desired sequence; for example, the oil may rst traverse the tubes I9, and then the tubes I'I, I8 and I6 in the order named and as indicated in Fig. 4. y

In the type furnace shown in Fig. 5, the roof tubes 20 which extend across the tops of the chambers G and H connected by the lopening 2| over the barrier or baille 22 receive heat by radiation from the flame issuing from the ignition or combustion chamber 23 and from the walls or lining of re chamber Gas well as by convection from the hot gases as they flow to chamber, zone or region I-I. 'I'he tubes 24 Within chamber H receive heat practically solely by'convection from the gases as they flow to stack S, or equivalent, though the upper tubes may also absorb substantial heat by radiation.

The heat input of tubes 20 may become excessive, particularly as they absorb heat both by radiation and convection. Tubes 20 are protected and the capacity of the apparatus materially increased by utilizing floor tubes, as tubes 26, to

, absorb heat from the combustion gases, lbelow which they are located, by radiation before they come into contact with the roof tubes 20, generally as above described.

The oil may enter the lower row of tubes 24a, pass upwardly through tubes 24h, then through the roof tubes 20, subsequently through the tubes 26 at the bottom of chamber G, and nally through the tubes 24o, though the sequence may be varied as desired.

The furnace shown in Fig. 6 is similar to that of Fig. 4 except that the heat source is different and the roof tubes I6 of chamber D are omitted. Instead of using a nozzle including a combustion chamber in which the air and fuel areforced by ejector or aspirator action independently of the stack draft, there is used what is or may be termed a Dutch-oven. Air induced by the stack draft mixes with fuel from the burner 21 within the chamber 28 and the mixture is heated by radiation from the lower part of the refractory wall W, the ame, and the refractory lining of the oven 29 in which the combustion reaction begins. By this arrangement, there is less probability of the floor tubes I9 absorbing heat to such great extent that the temperature of the gases and fuel is reduced below the combustion point in chamber D than if the combustible mixture or its components were directly introduced into chamber D for combustion therein. The floor tubes I9 as in Fig. 4 greatly increase the safe throughput of the apparatus without increase of furnace temperature.

In the modification of my invention shown in Fig. 7, combustion begins in the chamber 3 and the burning gases pass through the main re chamber B of the furnace and then through the done C which is essentially a duct leading to stack S. 'I'he tubes 8 in the zone C are heated preponderantly by convection, while the roof tubes 9 and the side wall tubes I0 of zone B, the main chamber of the furnace, are heated to substantial extent bothby radiation and convection. The tubes II on or adjacent the floor of the furnace are heated predominantly by radiation, both from the burning gases and to some extent from the upright walls of the furnace chamber which are free of tubes, with little or no absorption of heat by convection. 'I'he temperature of the gases is reduced to such extent by the heat absorption of tubes II that although the tubes 9 and I0 are heated both by radiation and convection, their temperature is not excessive. As in all modifications herein described, the rate of combustion and therefore the throughput may be materially increased beyond that otherwise possible Without tubes II or equivalent.

The oil may first pass through the tubes 8 of the zone C, then through the roof tubes 9, the tubes I0 of the left side wall, then the floor tubes I I, and finally the tubes I0 of the right hand side wall, the oil leaving the furnace from the upper tubes of this bank.

The furnace of Fig. 8 is similar in construction to'two furnaces such as shown in Fig. 3, arranged in opposition, the left hand side of the furnace of Fig. 8 being practically identical with Fig. 3 and the right hand end of the furnace being generally similar except that the zone A and tubes 6 have been omitted, although they may be used if desired, and in lieu thereof there are utilized the side tubes I0. The tubes 8 of zone'C absorb heat by convection from the gases from combustion chambers 3 and 3', the tubes 6 of zone A are heated practically solely by radiation from the refractory of the radiation combustion chambers 3, while the roof tubes 9 are heated both by radiation and convection from the flame as well as by radiation from the furnace refractory. Tubes I 0 are heated largely by radiation but may also be heated by convection to substantial extent. The main furnace chamber is divided substantially into two portions by the partition or baffle 25, and on either side of the partition and resting upon or adjacent the floor of each of the separately fired heating zones or lre chambers of the furnace are one or more rows of tubes II, which, as in the prior modifications, absorb sufiicient heat substantially solely by radiation from the gases so to reduce their temperature that the tubes 9 are not heated above their safe operating temperature for material increase in the combustion rate and throughput.

The furnace of Fig. 9 is similar to that of Figs; 4 and 6 with the exception'of the heat source. In this modification air and fuel from the burner alcance 30 are forced by injector action directly into the chamber D, the Venturi block 3l effecting intimate mixture of fuel and air. As the oor tubes I9 are in the zone of combustion reaction, I prefer to cover them with refractory 32 of suitable composition and thickness, for example silicon carbide, to insure that the cooling effect of the tubes will not reduce the temperature of the air and fuel in chamber D below the combustion point. By lnterposing refractory 32, the temperature at or adjacent the tubes may be several hundred degrees less than that of chamber D, but nevertheless, they absorb sufficient heat by radiation suitably to reduce the temperature to which the roof tubes I6 are subjected and permit of operation of the furnace at materially increased rating. As a less desirable alternative, the tubes I9 may be reduced in number.

In Fig. 10, there is contained in the boiler or shell still 33 the oil, or other material to be heated and operated upon therein in batches, or by more or less continuous feed to and withdrawal from shell 33. Hot and/or burning gases from the combustion chamber 34, similar to that of preceding modifications, or from any other suitable heat source, flow through the chamber I to the stack duct 35. The shell 33 absorbs heat both by radiation from the flame and refractory linings of chamber I and by convection from the flowing gases. Accordingly, there is danger of the heat-absorbing surface of the shell being raised to excessively high temperature. In accordance with my invention, tubes 36 are disposed within chamber I adjacent the floor and preferably spaced vtherefrom as by the supports or cross rails 31, to absorb heat principally by radiation suitably tol reduce the temperature of the gases striking the tank 33. 'I'hey also absorb some heat by convection, particularly at the end of the furnace where the gases pass downwardly to stack duct 35.

As shown, the oil or other liquid is passed through the pipes 36 connected to one or more perforated, distributing pipes 38, or equivalent, within shell 33 preferably adjacent the bottom thereof.

The use of auxiliary combustion chambers for projecting the combustion gases over the floor tubes is especially advantageous in connection with the furnaces of Figs. '7, 8 and 10, as in the furnace of Fig. 3 described above. In general, the auxiliary combustion chambers are effective to spread the hot combustion gases out into a uniform current over and above, as adjacently across the entire section of floor tubes and to effect a substantially uniform rate of heat-transfer per unit area to the entire bank of tubes.

It is characteristic of my invention that the safe throughput of a heat transfer system may be considerably increased merely by the addition of the floor tubes without increase of the furnace temperature, and with high economy, since excess air is not added to limit the operating temperatures, and with no increase in the size of the furnace. In general, the temperature to which heat-absorption structure of a furnace is subjected is maintained within safe operating limits by disposing tubes, or equivalent, below the path of the burning gases, as upon or adjacent the furnace fioor, to absorb heat, principally or solely by radiation, before the gases contact with any of the other heat absorption structure of the furnace. For example, the heat input of the floor tubes or equivalent may be as high as 20,000 B. t. u. per square foot of surface per hour.

The rate of transfer of heat is not diminished but o n the contrary high rate of heat transfer is sought. The average heat input is higher than heretofore realized as the rate of combustion may be increased without increase of the temperature to which heat absorption structure of any zone is subjected.

My invention is of particular importance to the art of cracking petroleum as it allows an increase of total heat input and correspondingly increased throughput Without localized overheating of any of the heat-absorption structure, particularly that absorbing heat both by radiation and convection.

With any of the furnaces shown, or with an type to which my invention may be applied, one or more additional rows or tiers of floor tubes may be utilized, and in all cases, the number of combustion chambers, burners, or equivalent will depend upon the amount of fuel that must be burned for the desired throughput, the five combustion chambers shown in Fig. 3A being illustrative, as many more, or less, may be used for different heat-input requirements.

In all modifications, the iioor tubes may be supported for substantially their entire length, as by the furnace floor, and since there is no need of supporting brackets, or the like, as in the case of tubes suspended from the roof or side walls, all of the tube surface capable of absorbing heat by radiation is exposed.

It is characteristic of my invention that by employment of the additional heat-absorption structure, generally in the form of tubes, located below the stream of hot gases or burning mixture, it absorbs heat largely or substantially solely by radiation, to effect such ,cooling of the gases that'in their further progress through the heat transfer system they will not cause or assist in causing excessive temperature rise.

By recourse to my invention, in a heat transfer system comprising a plurality of heat-absorption structures disposed in different regions or zones, by the employment of the so-called floor tubes hereinbefore referred to, the average heat input per unit of heat-absorption surface may be materially increased, without attainment of excessive temperature by any part of the heat-absorption structure, which, in the absence of the oor tubes or equivalent, would attain a temperature materially'in excess of the average temperature of the several absorption structures of the system.

The oor tubes absorb a substantial portion of the heat transferred by the entire system, and at the same time effect such cooling of the gases as to cause another portion or section of the entire heat transfer structure to operate at a temperature lower than that which would obtain in the absence of the floor tubes. By their use, for heat-absorption structures of the entire system of a given total heat-absorbing surface, the rate of combustion of fuel may be materially increased, imparting a greater. amount of heat per unit of time to the entire system, permitting greater throughput, with greater uniformity of temperature in and heat input into the several sections or zones, and without dangerous or excessive heating of any part of the heat-absorbing structure of the system.

I n general, the so-called floor tubes, such as Il, i9, 26, 36, are characterized by their position and by the fact that they absorb heat mainly or substantially solely by radiation. In general,

they are located outside of the stream` of hot gases, burning mixture or flames existing in or passing through the chamber in which the tubes are disposed, whereby they are not to substantial extent washed by moving gases; or, stated differently, the tubes are disposed in gas which is substantially 'at rest or having insubstantial velocity with respect to the tubes. The location of these so-called floor tubes is characterized by the fact that there is no tendency due to thermal or other action of the hot gases, burning mixture or flames, to impinge upon and wash the tubes. The hot gases, flames or burning mixture tend by natural thermal influence to rise, and the tendency to convective heating of the tubes is practically eliminated. The heat absorption is mainly or substantially solely by radiation directly from the hot or burning gases or flames, and/or the walls of the chamber, which in some cases attain temperatures rendering them sources of radiant heat, in contradistinction to the absorption of heat from radiating muiiies or enclosures for the burning mixture; and I have shown mufiies or combustion chambers within which combustion of fuel may be partially completed or substantially completed, nevertheless, some combustion of the products of combustion ordinarily occurs as the gases leave the tiring muiiies or combustion chambers. And in the claims I have used the expressions directly from the burning or still-burning gases the more accurately to describe the aforesaid heat absorption of the floor tube section, characteristic of the present invention and more particularly to exclude radiation from enclosing walls of muilles or combustion chambers 3.

While the invention herein described is generally similar to that shown in Letters Patent 1,591,431, it permits of operation of oil stills, or the like, at 4throughputs materially in excess of those practically attainable with the structures therein disclosed.

What I claim ts:

1. In an oil-cracking system the combination of oil heating apparatus comprising separate heat absorption structures disposed in different zones, means for producing a current of hot combustion gases through said zones in series and for heating the absorption structure in one of said zones by convection, all of the heat absorption structure of another of said zones disposed substantially entirely below and without the current of gases and adapted to absorb heat directly from said gases substantially solely by radiation.

2. Oil heating apparatus comprising heat absorption structure disposed in different zones, means for producing a current of initially burning combustion gases through said zones in succession, the heat absorption structure in one of said zones absorbing heat of said gases by convection and radiation, the heat absorption structure of another of said zones disposed substantially entirely below and without the current of gases and adapted to absorb heat directly from said initially burning gases substantially solely by radiation.

3. In a system of heating oil at least to distillation temperature. the combination of oil heating apparatus comprising a heating chamber traversed by burning combustion gases, a bank of roof tubes therein disposed to absorb heat by radiation and convection, a bank of oor tubes in said heating chamber disposed substantially entirely below and without the current of burning combustion gases exposed directly to radiation therefrom and heated lubstantially solely by radiation, and means for connecting said oor and roof tubes for passage of the oil therethrough in succession.

4. Oil heating apparatus comprising a chamber containing a source of heat comprising burning gases, a second chamber in communication with and traversed by hot gases from said first chamber, tubes in said second chamber containing oil to be heated and absorbing heat preponderably by convectton, tubes in said first chamber connected to said first tubes and absorbing heat by radiation and convection, and tubes connected to said other tubes and disposed adjacent the bottom of said first chamber below the path of said hot gases for absorbing heat directly from said burning gases substantially solely by radiation.

5. Oil heating apparatus comprising a heating chamber traversed by hot burning gases or products of combustion, roof tubes disposed within said heating chamber and absorbing heat directly from said burning gases by radiation and convection, and oor tubes disposed directly below the currents of hot gases or products of combustion for absorbing heat directly from said burning gases substantially solely by radiation, said tubes connected so that the oil therein flows through the said roof tubes and oor tubes in the order named.

6. Oil heating apparatus comprising a heating chamber traversed by currents of burning gases or products of combustion, roof tubes and side wall tubes disposed within said heating chamber and absorbing heat by radiation and convection, and floor tubes disposed below the currents of hot gases or products of combustion for absorbing heat directly from said currents of burning gases substantially solely by radiation, said tubes connected so that the oil therein ows through the said roof tubes, wall tubes, and oor tubes in the order named.

7. In an oil heating system in which, in at least one' zone, heat is transferred to oil-conducting heat-absorbing structure both by radiation and convection, the method of increasing the oil throughput of the system and heating itto desired discharge temperature, with moderated rate of application of heat per unit area per unit, time in different zones of the system which comprises producing a current of burning combustion gases, applying heat of said gases by radiation and convection to said structure, and limiting the rate of application of heat to said structure by heating another oil-conducting heat-absorbing structure in a zone below and without the current of gases substantially soleTy by-direct radiation from said burning gases at a rate per unit area substantially the same as the rate per unit area at which heat is applied to the oil by radiation and convection aforesaid.

8. In a furnace for heating hydrocarbon oils, a heating section, means for productng hot products of combustion for said heating section, a second heating section in its entirety positioned below said combustion producing means and receiving burning products of combustion therefrom, and separate heat absorbing tubes in said second heating section all of which are disposed below said combustion producing means and in open radiant view of, and below and substantially entirely without, the burning products of combustion therefrom and adapted to be heated substantially solely by radiant heat directly therefrom.

9. In an oil-heating system including a heating chamber having separate banks of oil-conducting heat-absorption tubes, with one of said banks disposed adjacent the floor and another adjacent the roof thereof, the method of heating oil to elevated discharge temperature which comprises directing a current of burning combustion gases of substantial initial velocity over and above and in avoidance of convective heat-transfer to, and in open radiant view of, said bank adjacent said floor, utilizing the directional eiTects upon said gases of their initial velocity and of their tendency to rise to keep them out of convective contact with said bank adjacent said iloor, directly transferring heat of said gases substantially solely by radiation to said bank adjacent said iioor, transferring heat of said gases by radiation and convection to said bank adjacent said roof, passing the oil through the tubes of one of said banks, and thereafter passing the oil through the tubes of the other of said banks.

10. In a system of heating oil to elevated discharge temperature, the combination of a heating compartment, upstanding baille structure dividing said compartment into a re chamber and a convection section, a bank of oil-conducting heatabsorbing tubes disposed adjacent the iioor of said fire chamber, means intermediate the roof and floor of said fire chamber for directing currents of burning combustion gases over and above and in avoidance of convective heat-transfer to said bank adjacent said floor, said lastnamed bank absorbing heat directly from said currents of gases substantially solely by radiation, a bank of oil-conducting heat-absorbing tubes disposed adjacent the roof of said fire chamber, and means interconnecting said banks for passage of oil through one of said banks and then through the other of said banks.

11. In a system of heating oil to cracking temperature, the combination of a heating compartment, upstanding baffle structure therein dividing said compartment into a re chamber and va convection section, tubular oil-conducting heat-absorption structures respectively disposed, one within said convection section, a second adjacent the roof of said iire chamber, and a third adjacent the floor of said fire chamber, means intermediate said roof and floor for directing currents of burning combustion gases over and above and in avoidance of convective heat-transfer to said structure adjacent said oor, said currents of gases traversing a path extending over and across said structure adjacent said floor, said last-named structure absorbing heat directly from said currents of gases substantially solely by radiation, and means interconnecting said structures for passage of oil rst through one and then through the remaining of said heat-absorption structures.

12. In an oil-heating system including a heating chamber having a bank of tubes disposed adjacent the floor thereof, the method of heating oil to elevated discharge temperature which comprises directing substantially entirely adjacently across, in open radiant view of and in avoidance of convective heat-transfer to, all of the tubes of said bank adjacent said iioor, a plurality of currents of burning combustion gases of substantial initial velocity and disposed side by side, utilizing the directional effects upon said gases of their initial velocity and of their tendency to rise to keep them out of convective contact with said tubes, transferring heat substantially solely by radiation directly from said plurality of currents of said burning gases to said tubes, and thereafter transferring heat at least in part by convection from said current of gases to tubular oil-conducttng heat-absorption structure within a zone of the system traversed by said current of gases.

13. The method of heating oil to cracking temperature in a system in which heat is applied to the oil by different modes of heat-transfer in different zones while iiowing in succession through tubular oil-conducting heat-absorption structures within said zones which comprises, producing currents of hot gases through said zones, in one of said zones applying heat of said gases to the oil-conducting structure therein by radiation and convection, in a second of said zones directly below said one of said zones andA below and without said currents of gases applying heat directly to the oil-conducting structure therein substantially solely by radiation from said gases at such rate per unit of area of heatabsorption surface per unit of time as to substantially equalize the rate of application of heat to one with respect to the rate of application of heat to the other of said structures.

14. In an oil-heating system, a ilre chamber having oil-conducting heat-absorption structures disposed adjacent the roof and iioor thereof, the method of heating oil to elevated discharge temperature which comprises directing intermediate said structures and above and in avoidance of convective heat-transfer to the structure adjacent said oor, a current of burning combustion gases, transferring heat directly from said gases by radiation and convection to the structure adjacent said roof, transferring heat directly from said current of gases substantially solely by radiation to the structure adjacent said floor at a rate per unit of time per unit of area of heat-absorption surface substantially to equalize the heat input to one with respect to the heat input to the other of said structures, and thereafter transferring heat of said gases by convection to heat-absorption structure within a zone of the system traversed by said gases from said dre chamber.

15. In a furnace for heating hydrocarbon oils, a combustion chamber having means for produc- Iing hot products of combustion associated therewith, a heating chamber connected to said combustion chamber for receiving hot products of combustion therefrom, and a bank of conduit elements for conveying oil being heated in said heating chamber arranged in parallel relation-l ship to each other in a substantially horizontal plane and in its entirety disposed below and substantially entirely, without the current of hot products of combustion and adapted to absorb 'heat directly from said hot products of combustion substantially solely by radiant heat.

16. Oil heating apparatus comprising a heating chamber, a combustion chamber discharging hot combustion gases into said heating chamber, a bank of tubes disposed in said heating chamber adjacent an upright wall whose surface is generally normal to the direction of the discharge of gases from said combustion chamber into said heating chamber, a bank of floor tubes in said heating chamber heated substantially solely by radiation disposed substantially entirely below and without the current of gases discharged from `said combustion chamber into said heating chamber and adapted to absorb radiant heat directly from said gases, and means for connecting said wall and iloor tubes for passage of the oil therethrough in succession.

17. An oil heating system comprising a combustion chamber, a heating chamber into the lower portion thereof said combustion chamber discharges still-burning gases to effect a current thereof in said heating chamber, tubular oilconducting heat-absorbing structure in said chamber disposed to receive heat from the gaseschamber into which said combustion chamber discharges hot gases and extending upwardly above the outlet of said combustion chamber, heat absorption structure disposed to receive heat from the gases by convection, a separate iioor tube section disposed in said heating chamber without the current of gases below said outlet and heated substantially solely by radiation directly from said gases, and means for connecting said iioor tube section and heat absorption structure for passage therethrough of the fluid to be heated.

19. A system for transferring heat to a,fluid passed through heat absorption structures, -comprising a radiation combustion chamber, heat absorption structure receiving heat preponderantly by radiation from the Wall of said combustion chamber, a heating chamber into which said radiation combustion chamber discharges hot gases and extending upwardly above the outlet thereof, heat absorption structure disposed in the current of gases to receive heat therefrom by convection, a floor tube section disposed in said heating chamber without the current of gases and heated substantially solely by radiation directly from said gases, and means for connecting said floor tube section and heat absorption structures for passage therethrough of the iiuid to be heated.

20. A system for transferring heat to a hydrocarbon fluid passed through heat absorption structures, comprising a heating chamber, a horizontal combustion chamber, having a length at least several times its height, disposed in the lower portion of said heating chamber above its viioor, heat absorption structure in said chamber at least a portion of which is disposed above the discharge of said combustion chamber to receive heat from the gases by convection, a floor tube section disposed in said heating chamber below the discharge of said combustion chamber and heated directly from the hot gases substantially` solely by radiation, and means for connecting said oor tube section and said heat absorption structure for passage therethrough of the uid to be heated.

21. In an oil-cracking system, the combination of means for transferring heat to fluid comprising a chamber, combustion chambers side by side discharging initially burning combustion gases into said chamber, heat absorption structure disposed in said first-named chamber comprising a bank of tubes, at least some of which are adjacent the discharge of said combustion chamber substantially without the stream of gases discharged from said combustion chamber and all of which are substantially entirely below the discharge of said combustion chamber, adapted to absorb heat substantially solely by radiation directly from' said burning gases, heat absorption structure in another zone of the system adapted to absorb heat by convection from said combustion gases, and means for connecting said heat absorption structures for passage of the iiuid therethrough.

22. A system for transferring heat to fluid comprising a chamber, a combustion chamber discharging burning combustion gases into and laterally across said chamber, tubular heat absorption structure in said chamber disposed transversely to and substantially entirely below and without the stream of gases discharged from said combustion chamber exposed directly to radiation from said gases and heated substantially solely by radiation, another tubular heat absorption structure in said system adapted to absorb heat by convection from the combustion gases, and means serially connecting said heat absorption structures for passage of the iiuid therethrough.

23. Petroleum cracking apparatus comprising a combustion chamber, a heating chamber into the lower portion whereof said combustion chamber discharges burning gases to effect a current thereof through said heating chamber, tubular petroleum-conducting heat-absorbing structure disposedto receive heat from the gases in at least substantial part by convection, and means for limiting the temperature to which said rstnamed tubular structure is heated by said gases comprising tubular petroleum-conducting heatabsorbing structure disposed substantially entirely below the discharge from said combustion chamber and in a substantially horizontal plane and below and without and transverse to said current of burning gases to absorb heat directly from said gases substantially solely by radiation.

24. Heat transfer apparatus comprising a combustion chamber within which fuel is partially burned, a heating chamber in communication with the discharge of said combustion chamber and into which said combustion chamber discharges still-burning gases, heat-absorption structure within said heating chamber and heated by radiation and by convection, other heat-absorption structure in said heating chamber in its entirety disposed beneath and substantially entirely without the current of gases and immediately adjacent and below the discharge end of said combustion chamber, and exposed directly to the radiation from said gases and heated substantially solely by radiation, for limiting the temperature to which the rst-named heat-absorption structure is subjected.

25. Oil heating apparatus comprising a combustion chamber, a heating chamber in communication with the discharge end of said combustion chamber and traversed by the hot burning gases and products of combustion, a bank of tubes heated by radiation and convection disposed in a single row within and adjacent the roof of said heating chamber, another bank of tubes heated by radiation and convection disposed in a single row within and adjacent a side wall of the heating chamber opposite the discharge end of said combustion chamber, and means for reducing the temperature of said gases and products of combustion to prevent excessive temperature of the tubes of said banks, comprising floor tubes connected with said banks of tubes and disposed without the stream of hot burning gases and products oi' combustion for absorbing heat directly therefrom substantially solely by radiation.

26. .Oil heating apparatus for heating oil to cracking temperature comprising a chamber, means for introducing burning combustion gases into the lower portion of said chamber to eil'ect a current of hot gases through said chamber, heat absorption structure in said chamber adapted to absorb heat by convection and radiation from said gases', and means for reducing the temperature of said gases to prevent excessive temperature of said heat absorption structure comprising another heat absorption structure disposed in said chamber below the entry of said combustion gases into said chamber without said current of gases and in open radiant view therewith and absorbing heat directly from said burning gases substantially solely by radiation, and means for serially connecting said heat absorption structures for passage of the oil therethrough.

27. Ihe method of heating oil which comprises effecting combustion largely completed in a combustion chamber, discharging burning gases from said chamber to effect a current of hot gases through zones in series and through which the oil passes in succession, in one of said zones applying heat to said gases to oil-conducting heat-absorbing structure by convection and radiation, and in a zone below the discharge from said combustion chamber and without said current of burning gases applying heat directly from said burning gases to another oil-conducting heat-absorbing structure substantially solely by radiation at such rate per unit area, relative to the rate per unit area per unit time at which heat is applied to the oil in said rst named zone,`that the application of heat per unit area per unit time in said zones is rendered practically uniform.

28. An oil heating system comprising a heating chamber, a combustion chamber, means for effecting substantially complete combustion of fuel in said combustion chamber which discharges into the lower portion of said heating chamber to eiect a current of initially still-burning gases in said heating chamber, tubular oil-conducting heat absorbing structure disposed in said heating chamber to receive heat from the gases by convection and radiation, and means for limiting the temperature to which said first named tubular structure is heated by said gases comprising tubular oil-conducting heat absorbing structure disposed horizontally across said heating chamber and below the discharge from said combustion chamber and without said current of gases to absorb heat directly from said current of burning gases substantially solely by radiation.

29. A system for heating petroleum, comprising a housing structure enclosing a plurality of heating zones, a plurality of heat absorption structures disposed in different of said zones, of said zones being directly above another of said zones, means for connecting said absorption structures for passage of the petroleum therethrough in successton, a combustion chamber discharging still-burning combustion gases through said zones, heat absorption structure in said one of said zones adapted to be heated by radiation and convection, and tubular heat absorption structure in the other of said zones disposed substantially entirely below and without the stream oi gases from said combustion chamber, exposed directly to radiation from said still-burning gases and heated substantially solely by radiation from said gases.

30. In-an oil heating system in which heat is transferred to the oil by different modes of heat transfer in different zones while flowing in succession through banks of tubes within said zones, the method of heating the oil to cracking temperature which comprises effecting combustion in a chamber, discharging still-burning gases from said chamber in a current directed adjacently across and entirely above all the tubes Within a first of said zones, substantiallysolely by radiation transferring heat directly from said current of gases to all said tubes before transfer of heat from said gases by radiation and convection, and in another of said zones transferring heat by radiation and convection from said gases to another of said banks of tubes.

31. Heat transfer apparatus comprising a heating chamber traversed by burning gases, heat-absorption structure disposed in said chamber and absorbing heat by radiation and convection from said gases, other heat-absorption structure disposed adjacent the bottom of said chamber and all of which structure is substantially entirely beneath and exposed directly to radiation from said gasesv and heated substantially solely by radiation and so disposed differently, in relation to the gas flow, from said first named absorption structure that it absorbs sufficient heat materially to reduce the temperature of said gases for protection of said rst heat-absorption structure, and means for preventing cooling of vsaid gases by said other heat-absorption structure below the temperature of combustion, comprising a chamber for effecting at least partial combustion before introduction of said gases into said heating chamber.

32. Oil treating apparatus comprising a heating chamber, a tank containing oil to be heated disposed at least in part within said chamber for absorption of heat by radiation and convection, and tubes in communication with said tank through which the oil is passed disposed adjacent the bottom-of said chamber for absorption of heat substantially solely by radiation.

33. An apparatus for heating hydrocarbon oils in cracking processes comprising a furnace chamber having end and side walls, a flue outlet at the top of the furnace chamber at one end thereof, combustion tunnels adjacent the bottom of the furnace chamber immediately below the flue outlet, a bank of tubes disposed in the path of combustion gases moving toward said ue outlet, a shield disposed below said bank of tubes, radiant tubes positioned below said shield and above said combustion tunnels, additional radiant heat tubes arranged along the floor of the furnace chamber in advance of and below the level of said combustion tunnels and below and in open radiant view of still-burning combustion gases discharged from said tunnels to absorb heat directly from said gases substantially solely by radiation, and additional tubes positioned beneath the roof of the furnace chamber.

34. Oil heating apparatus comprising a plurality of chambers, means for each of said chambers for maintaining therein currents, of burning combustion gases, individual to said chambers, a bank of oil-conducting tubes in each of said chambers positioned with al1 its tubes beneath and substantially without the gas current therein and exposed directly thereto and heated substantially solely by radiation therefrom, tubular oil-conducting heat absorption structure convectively heated by a gas stream comprising gases of said gas currents individual to said chambers, and means connecting said banks and said structure for passage of oil through said convectively heated structure, through one, and thereafter 'through the other, of said banks of tubes.

35.011 heating apparatus comprising a plurality of chambers, means for each of said chambers for maintaining therein currents, of burning combustion gases, individual to said chambers, a bank of oil-conducting heat absorption structure tubes in each of said chambers heated by both radiation and convection, a separate bank of oil-conducting heat absorption tubes in each of said chambers disposed with all its .tubes beneath and substantially entirely without the gas current therein and absorbing heat directly from said burning gases substantially vsolely by radiation, a bank of oil-conducting heat absorption tubes convectively heated by a gas'stream comprising gases of said currents individual to said chambers, and means serially connecting said banks of tubes for passage of oil first through said convectively heated bank and then through each of the remaining of said banks.

36. Oil heating apparatus comprising a plurality of chambers disposed end to end, a combustion chamber for each of said chambers discharging therein a current, of still-burning combustion gases, individual thereto, and oil-conducting heat absorption structure in each of said chambers disposed in open radiant View of and below the current of gases discharged from the combustion chamber individual to said chamber and absorbing heat directly from said stillburning gases substantially solely by radiation.

37. Oil heating apparatus comprising a furnace chamber, baiile structure upstanding therein and dividing it into heating chambers in communication above the balile structure, means for each of said heating chambers for maintaining therein currents, of burning combustion gases, individual to said heating chambers, a bank of oil-conducting heat absorption tubes in each of said heating chambers positioned with all its tubes in open radiant view of, beneath and substantially without, the gas current therein and absorbing heat directly from said burning gases substantially solely by radiation, tubular oilconducting heat absorption structure convectively heated by a gas stream comprising gases of said currents individual to said heating chambers, and means connecting said structure and said banks for passage of oil rst through one of said banks and then through the other of said banks.

38. In an oil-cracking system, heating apparatus comprising a plurality of chambers, means for maintaining therein currents of burning com.- bustion gases individual to said chambers, a bank of oil-conducting tubes in eachy of said chambers disposed with all its tubes directly exposed to and positioned beneath and substantially without the gas current therein and absorbing heat directly from said burning gases substantially solely by radiation, tubular oilcpnducting heat absorption structure convectively heated by a gas stream comprising gases of said gas currents individual to said chambers, and means connecting said banks and said structure for passage of oil rst through said heatabsorption structure and then through one and then through the other of said banks of tubes.

39. Oil heating apparatus comprising a single heating compartment, baille structure dividing it into a plurality of heating chambers disposed A heating compartment, baille structure upstanding therein and dividing it into a plurality of heating chambers disposed end-to-end and in communication above the baille structure, combustion chambers adjacent the opposite ends of said compartment and respectively7 discharging into said heating chambers currents of sti1l burning combustion gases individual thereto, a bank of floor tubes disposed below and without each of the respective currents of said gases and absorbing heat directly from said burning gases substantially solely by radiation, and at least one additional bank of tubes arranged Within the combined currents of gases from said combustion chambers.

41. Oil heating apparatus comprising a single heating compartment, baille structure therein and dividing it into a plurality of heating chambers disposed end-to-end and in communication around the baille structure, combustion chambers disposed at the opposite ends ol said compartment and discharging into each of said chambers a current, of still-burning combustion gases, individual thereto, a bank of floor tubes in each of said heating chambers disposed below the current of gases discharged from its associated combustion chamber and heated directly from said gases substantially solely by radiation, a bank of roof tubes arranged adjacent the roof of both of said heating chambers, and means connecting said banks of tubes for passage of oil therethrough.

42. Oil heating apparatus comprising a single heating compartment, baille structure therein dividing it into a plurality of heating chambers disposed endto-end in communication around the baille structure, combustion chambers disposed atthe opposite ends of said compartment and discharging into each of said chambers a current, of-still-burning combustion gases, individual thereto, a bank of oor tubes in each of said heating chambers disposed below the current of gases discharged from the associated combustion chamber and absorbing heat directly from said still-burning gases substantially solely by radiation, a bank of roof tubes arranged adjacent the roof structure of said compartment, a bank of tubes convectively heated by a gas stream comprising gases of said gas currents individual to said heating chambers, and means for connecting said banks of tubes for passage of oil rst through one and then through the remaining of said banks.

43. Oil heating apparatus comprising a single heating compartment, at least one intermediate Wall therein dividing it into a plurality of heating chambers disposed end-to-end and in communication above said wall, combustion chambers associated with opposite walls of said compartment and discharging into said chambers currents of still-burning combustion gases, individual to said chambers and directed towards said intermediate wall, and combining, a bank disposed below the respective currents of gases discharged from said combustion chambers and absorbing heat directly from said still-burning gases substantially solely by radiation, at least one bank of side wall tubes, a bank of tubes arranged adjacent the roof structure of said compartment and substantially above said intermediate wall and heated by combined convection and radiation, and a bank of tubes arrange Within the combined currents of gases from said combustion chambers for absorption of heat by convection.

44. Oil heating apparatus comprising a heating compartment, baille structure dividing it into a plurality of heating chambers disposed end-toend and in communication around the baille structure, means associated with each of said chambers for maintaining therein currents, of burning combustion gases, individual thereto, a bank of tubes in each of said chambers disposed to absorb heat directly from said burning gases substantially solely by radiation, a gas passage adjacent one end of said compartment, one of said heating chambers intervening between another of said heating chambers and said passage, the gases from said other heating chamber passing around said baille structure and through said passage in mixture with the gases from said one chamber, a bank of tubes disposed in said passage and absorbing heat from said gases by con- Vection, and means connecting said banks of tubes for passage of oil first through one and then through the remaining of said banks of tubes.

45. Oil heating apparatus comprising a heating compartment, upstanding baille structure dividing the compartment into a plurality of heating chambers disposed end-to-end and in communication above said baille structure, means associated with each of said chambers for malntaining therein currents of burning combustion gases individual thereto, a bank of roof tubes in each of said chambers, a bank of tubes in each of said chambers without the current of gases individual thereto and disposed to absorb heat directly from said burning gases substantially solely by radiation, a gas passage adjacent one end of said compartment, one of said heating chambers intervening between another of said heating chambers and said passage, the gases. from said other heating chamber passing above said baille structure and through said passage in mixture with the gases from said one chamber, a bank of tubes disposed in said passage and heated by convection, and means connecting said banks of tubes for passage of oil rst through said lastnamed bank and then through each of said remaining banks of tubes.

46. A system of heating oil to oil-cracking discharge temperature comprising a pair of opposed heating chambers, means including combustion chambers individual to said heating chambers for maintaining therein currents of still-burning combustion gases, tubular oil-conducting heatabsorption structure disposed in each of said heating chambers lin open radiant view of, and substantially entirely below and without, the gas current therein and directly heated thereby substantially solely by radiation, a third heating chamber connected to said pair of heating chambers and traversed by the combined currents of gases therefrom, tubular oil-conducting heatabsorption structure disposed in said third chamber, and means connecting said structures for passage of oil first through said structure in said third chamber and then in succession through said structures in said pair of chambers.

47. A system of heating oil to oil-cracking discharge temperature comprising a pair of opposed heating chambers, means individual to said 'chambers for maintaining therein currents of burning combustion gases initially spaced laterally from each other, tubular oil-conducting heatabsorption structure disposed in each of said chambers in open radiant View of, and substantially entirely below and without, said currents of gases therein and heated directly substantially solely by radiation from said currents of gases, other tubular oil-conducting heat-absorption structure disposed in each of said chambers to be heated by radiation and convection from said `currents of gases, a third heating chamber connected to said pair of chambers and traversed by the combined currents of gases therefrom, tubular oil-co-nducting heat-absorption structure disposed in said third chamber to be heated by convection, and means connecting said tubular structures for passage of oil first through said convectively heated structure, and then in direct suc- 'cession through the remaining of said tubular structures disposed in said pair of chambers.

Y48. A system of hea-ting oil to cracking temperature comprising a pair of opposed heating chambers, means individual to said chambers for maintaining therein currents of burning combustion gases, tubular oil-conducting heat-absorption structure disposed in each of said chambers adjacent the floor thereof in open radiant view of, and substantially entirely below and without, said -currents of gases burning therein and directly heated therefromsubstantially solely by radiant heat, other tubular oil-'conducting heat-absorption structure disposed in each of said chambers adjacent the roof thereof and absorbing heat from said gases by radiation and convection, a third heating chamber connected to said pair of chambers and traversed by the combined currents of gases therefrom, tubular oil-conducting heat-absorption structure disposed in the gas stream in said third chamber to be heated by convection, and means interconnecting said tubular structures for serial passage of oil through all of said structures and providing for passage of the oil in direct succession through said tubular structures Within one of said pair of chambers.

49. In an oil heating system including a furnace having a pair of separately fired heating zones and a convection zone receiving the combustion gases from both the heating zones, the method of heating hydrocarbon fluid which comprises passing it in succession through banks of `fioor tubes in each of said heating zones, in open -gases within each of said heating zones above and in positive avoidance of the floor tubes directly, transferring heat substantially solely by radiation from the currents of hot gases to the oor tubes therebeneath, passing the hydrocarbon fluid through said convection zone before its said passage through each of said banks of floor tubes, and in said convection zone transferring heat by convection to said fluid from the combined currents of gases.

50. In an oil heating system including a furnace having a convection zone, and a heating chamber divided by baflle structure into separately fired heating zones, said convection zone receiving the combustion gases from both heating zones, the method of heating oil to oil-,cracking discharge temperature which comprises passing it through one and then through the other of separate banks of floor tubes disposed respectively in said heating zones, projecting over and above and in open radiant view of said banks of floor tubes in each of said heating zones currents of burning combustion gases of substantial initial velocity, in each of said heating zones utilizing both the effect upon said gases of their initial velocity and the forces producing rise of ea'ch said current to rmaintain the current within each of said heating zones above and in positive avoidance of the floor tubes, directly transferring heat of said burning currents of gases substantially solely by radiation to the floor tubes therebeneath, passing the oil through said convection zone and through at least a part of one of said heating Zones prior to its said passage through each of said banks of floor tubes, and in said convection zone transferring heat by convection from said gases to the oil.

FRANK H. PRAEGER.

CERTIFICATE OF CORRECTION.

Patent No. 2,129,589. i September 6, 1958.

FRANK H. PRAEGER.

1t ishereby certified that error appears in the` printed specification of the' above numbered patent re quring correction as follows: Page l, second column, line 2)a for the word "burner" read burned; page 5, first column, line 16, for "tube" read tubes; page 5, second column, line )42, for "ts" read is; page 6, first column, line 9-10, claim L, for "preponderably" read preponderantly; line lO, same claim, for "convectton" read convection; line M8, claim?, after "unit" strike out the comma; line )19, same claim, after system inserta comma; page 7, first column, line 5, claim l2, for "oilconducttng" read oil-conducting; and second column, line 5, claim l?, for

"thereof read whereof; page 8, second column, line 2T, claim 2?, for "to" first occurrence, read of; line 55, same claim, strike out the words "per unit time" and insert the same after "area and before the comma in line 5) same claim 27; line 60, claim 29, after uzones," insert one; line 6) same claim, for "successtonu read succession; line 69, same claim 29, after "zones" insert a comma; page 9, second column, line 9, claim 55', Strike out the word "structureg page 1l, first column, 1ine 12, claim 1,7, 1 for uheated directly" read directly heated; line 55, claim )18, for "gases burning" read burning gases; and second column, line 16, claim )49, after the syllable "rectly" strike out the comma and insert the same after "tubes", line l5,

same claim; and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office.

Signed'fand sealed this 25th day of October, A. D. 1958.

- Henry Van Arsdale (Seal) Acting Commissioner of Patents. 

